Smell gas but no leak?

We had a boiler fitted in September ( in a cupboard in my DS's bedroom) and we have been smelling gas sporadically ever since. In October I opened the cupboard to a really strong smell so rang the emergency line who came tested for a leak ( there was a drop of 2 on the test thing) he said this alone was not a problem but due to the smell cut us off. We tried to contact company who fitted the boiler but couldn't as it was the weekend. British gas came out and couldn't find any probs but tightened all the joints up.After a few more smells wafting around rang plumbers who fitted boiler and they came round straight away. He tested for leaks and there was a drop of 1. He said this was not a problem as you can have a drop of 6. He suggested that the smell could be due to a hole in the ceiling of the cupboard into the loft ( where the old pipes used to be) and we are getting smells from the outlet floating into the eaves and down the hole. Very draughty house and the outlet/ vent is close. Is this realistic? Really concerned but no leaks apparently. Don't know what to do as nobody else can find a problem. Any suggestions?

you could go up into the loft while the boiler is running and see if you think there is an atom of truth in the idea.

you could seal the hole into the loft, though I won't be surprised if that makes the smell worse. I would suspect that the leak is on a gas pipe near the boiler, so closing the ceiling will prevent it getting out.

I can be of no help but share your frustration/concern. We keep getting a whiff of gas around our gas fire, plumber said there are no leaks but I can definitely smell it. I think ours coincides with when it is quite windy outside

Sorry I don't know. I thought the manometer test was 'no discernable drop' but I am not a gasman.

I can envisage putting a valve in the supply pipe to the boiler to see if the leak is upstream or downstream of the valve, but it might take a lot of work, and who would pay? I suppose they have already tried turning off the valve under the boiler.

p.s.If the pipe runs under the floor it is always worth lifting a board and having a sniff. You can make your own leak finder by putting a drop of WUL in a plant mister with water and spraying any suspect joints. Escaping gas will form a bubble. I like to clean all joints with a green pan scourer so the copper pipe is clean and bright, but that is more helpful to identify water leaks which will leave a green or white deposit.

on many modern boilers there will be a yellow T or Lever handle valve to turn the gas off. If you are going away for a few days you could turn that off, and see if the smell has stopped when you come back. That will tell you if the leak is on the boiler side of that valve (it is very unlikely, because everything above the valve is assembled in the factory). Might be worth a try if they did not already try turning off when doing the pressure test.

You may have to go through a reset or restart process per the instruction book when you come back, so maybe wait for the warmer weather.